1. Field of the Invention
The present invention generally relates to access performance adjusting methods and storage apparatuses, and more particularly to an access performance adjusting method for adjusting a sequential access performance and a random access performance with respect to a recording medium, and to a storage apparatus which employs such an access performance adjusting method.
2. Description of the Related Art
In a magnetic disk apparatus which uses a magnetic disk having concentric tracks on which data are recorded, a sequential access is carried out to sequentially access a plurality of tracks. In order to carry out a data transfer at a high rate when carrying out the sequential access, the so-called “skew” technique is used. The skew technique shifts a data write starting position of each track depending on a time (hereinafter referred to as a head moving time) it takes to move a head from one track to another.
For example, suppose that the skew technique is not used and the data access starting positions of two mutually adjacent tracks are physically located along the same radial direction. In this case, when the access to the first track is completed and the head is to move to the adjacent second track, the head cannot move to the data access starting position of the second track in time, and it becomes necessary to wait for the magnetic disk to undergo one revolution. In other words, a wait time is generated. But when the skew technique is used, the data access starting position of the second track is shifted from the data access starting position of the first track in a circumferential direction by an amount corresponding to the head moving time, so as to reduce the wait time. When using the skew technique, the access performance is improved by reducing a data access delay caused by the wait time. Hence, an amount of skew, when converted in time, is set so that a minimum value becomes equal to the head moving time between two mutually adjacent tracks.
On the other hand, the magnetic disk apparatus uses a technique called “defective track avoiding process” to avoid defective tracks existing on the magnetic disk. When a defective track is detected on the magnetic disk, this defective track avoiding process avoids the defective track by preparing and using an alternate track on an inner peripheral side of the defective track, so as to maintain the total number of tracks constant among the magnetic disk apparatuses.
The recording density of the magnetic disk apparatus is increasing every year, and systems have been proposed to variably set the recording density, such as a Bit Per Inch (BPI) or a Track Per Inch (TPI) depending on the capabilities of the head and the magnetic disk. The yield of the magnetic disk apparatus can be improved by variably setting the BPI or TPI to an optimum value with respect to each combination of the head and the magnetic disk. However, when such a system is employed, the number of sectors within the track and the number of cylinders become different for each combination of the head and the magnetic disk and/or for each magnetic disk apparatus. The variable setting of the BPI or TPI is not made by the user, and is made when shipping the magnetic disk apparatus.
In the magnetic disk apparatus having the recording density, such as the BPI and TPI, that is variably set, the data transfer rate becomes different for each head and/or for each magnetic disk apparatus. For this reason, even among the magnetic disk apparatuses having the same storage capacity, there was a first problem in that the sequential access performance becomes greatly different among the magnetic disk apparatuses.
In addition, when the defective track avoiding process is carried out, the track that is used shifts towards the inner peripheral side of the magnetic disk. Consequently, if the defective tracks are frequently detected on a specific magnetic disk in the magnetic disk apparatus having a plurality of magnetic disks, a data storage location on the specific magnetic disk becomes greatly different from the corresponding data storage locations on the other magnetic disks within the magnetic disk apparatus. As a result, compared to the magnetic disks on which the defective tracks are not detected, the seek distance of the head with respect to the specific magnetic disk becomes longer. Accordingly, there was a second problem in that the random access performance with respect to an arbitrary track becomes greatly different among the magnetic disks within the magnetic disk apparatus depending on the number of defective tracks, and that the random access performance becomes greatly different among the magnetic disk apparatuses having the same storage capacity due to similar reasons.
Moreover, in the magnetic disk apparatus having the recording density, such as the BPI and TPI, that is variably set, the cylinder width at the time when one track is avoided becomes different for each head and/or for each magnetic disk apparatus, and the difference in the physical positions of the cylinders increases among the heads. Therefore, there was a third problem in that the random access performance becomes greatly different among the magnetic disk apparatuses, even among the magnetic disk apparatuses having the same storage capacity.
The first through third problems described above were not only generated in the magnetic disk apparatuses, but also in storage apparatuses having various kinds of recording media, such as optical disk apparatuses and magneto-optic disk apparatuses.